Safety paper and method of making safety paper



P 1938. F. L. siMQNs ET AL 2,129,362

SAFETY PAPER AND METHOD OF MAKING SAFETY PAPER Filed NOV. 21, 1936 0 1N ENTORS ATTORNEYS Patented Sept. 6, 1938 UNITED STATES SAFETY PAPER AND METHOD OF MAKING SAFETY PAPER Francis L. Simons, Needham, and Mark W. Weiss, Boston, Mass, assignors to George La Monte & Son, Nutley, N. J., a corporation of New Jersey Application November 21, 1936, Serial No. 112,008

20 Claims.

This invention relates to safety paper and method of making safety paper. This invention relates particularly to paper of the type which, by appropriate treatment, can be tested to determine its authenticity. According to this invention, a safety paper is afforded which when treated with a liquid, as, for example, by moistening a portion of the same with water, will give visible evidence of its authenticity.

Safety paper of the type to which this invention relates is suitable for many purposes. For example, safety paper of the type to which this invention relates is adapted for use in connection with labels, tickets, wrapping papers, boxboard for cartons, and the like, so that the genuineness thereof may be determined. To illustrate, safety paper embodying this invention is adapted for use .as the paper for labels for beverages. In connection with the sale of alcoholic beverages, certain unscrupulous sellers have manufactured counterfeit labels bearing the names of wellknown liquors commanding a relatively high price and have applied them to inferior and inexpensive liquors. According to the present invention, safety paper is afforded which enables one to determine in a convenient, positive and simple manner whether such labels, for example, are genuine or counterfeit. Labels embodying this invention can be made which in normal appearance resemble the labels of ordinary character. However, merely upon applying a liquid, 6. g., water, to the label or to a portion thereof, visible evidence of the genuineness of the label is at once appparent. After the label has dried again, is preferably assumes its original appearance.

It is a purpose of the present invention to afford an improved safety paper of the character above mentioned and an improved method for the manufacture of such safety paper.

Safety paper embodying this invention comprises a plurality of layers. invention, a subsurface layer and a surface layer which overlies the subsurface layer are of contrasting color. Preferably the subsurface layer is of a dark shade such as a deep shade of some primary color. The surface layer which overlies the colored subsurface layer is of some color which contrasts with the color of the subsurface layer either by being of a different color or by being of a less intense color. If a white label is desired, the surface layer is White. It is a feature of the present invention that the surface layer comprises first and second portions which are of different character as far as their response to treatment with a liquid is concerned. The first According to this portion of the surface layer is composed of material which is adapted to have its permeability to light substantially increased by the application of a liquid, e. g., water, thereto, so that the color of the subsurface layer is visible by being rendered visible after having been completely obscured or by becoming substantially more visible after have been partly obscured. The second portion of the surface layer is of such character that, when the paper is treated with the liquid which makes the first portion of the surface layer more permeable to light, the second portion remains substantiallyunaffected or else is affected in a substantially less degree than the first portion. Preferably the second portion of the surface layer is in the form of desired legends or other indicia such as lettering, numbers, or the like.

To afford one example of paper embodying this invention, such paper may be manufactured by first preparing a sheet of material which is.

to constitute a subsurface layer of the safety paper. As aforesaid, this layer preferably is colored as by including a pigment or dye. Over this subsurface layer, a surface layer is applied which may consist of some composition such as a mixture of casein and clay or some fibrous mixture which is of such character as to have its permeability to light substantially increased when the dry material has a liquid, e. g., water, applied thereto. A sealing material is then applied to some portion or portions of the surface layer, leaving other portions untreated. Preferably the sealing material is applied by a printing operation in the form of a plurality of legends or other suitable indicia using a sealing material which does not substantially alter the color of the material of the surface layer. For example, some sealing material such as linseed oil or a clear lithe-varnish can be applied to the safety paper in this manner. It is apparent that wherever the sealing material is applied to the surface layer, such portion is adapted to be substantially less affected upon the application of the testing liquid,

e. g., water, thereto than the remaining portion or 4 portions of the surface layer of the safety paper to which the sealing material has not been applied. Safety paper embodying this invention can be finished and printed upon the same as ordinary paper and can be made up into labels, tickets and the like of the character aforesaid.

When it is desired to test a paper of the character aforesaid, all that is necessary is to apply a testing liquid such as water to at least a portion of the paper. Upon the application of the testing liquid, the portion of the surface layer which has not been treated with the waterproofing material becomes permeable to light so that the colored subsurface layer is visible therethrough.

However, those areas or portions of the surface layer which include the sealing material do not become as permeable to li-ghtas the remainder of the surface layer and consequently those areas or portions (which may be in the form of letters or numbers, for example) stand out prominently against a background of contrasting color. When the paper dries, the surface layer in its entirety preferably reverts to its original impermeability to light and assumes its normal substantially uniform appearance.

Safety paper embodying this invention may be used with or without ordinary printing applied to the surface thereof (although permanent allover solid color printing preferably is not employed). Normally in the production of labels, tickets and. the like, printing in the form of trade-marks and the like is applied to the surface of the paper. Such printing does not in any way interfere with the testing of the paper by the application of a liquid. thereto as hereinabove mentioned.

Further purposes, advantages and features of this invention will be apparent from the following description of this invention in connection with theaccompanying drawing which shows certain illustrative embodiments thereof, wherein:

Fig. 1 is ,a plan view of safety paper embodying this invention;

Fig. 2 is a view of the safety paper shown in 1 Fig. 1 whichillustrates a color change developed upon-the application of a testing liquid thereto;

Fig. 3 is a cross-section of the safety paper shown in Figs. 1 and 2;

Fig. l is acrpss-section of an alternative type of safety'paper embodying this invention;

' Fig. 5 is a cross-section of a further alternative type of safety paper embodying this invention; and

i Fig. 6 is a cross-section of a still further alternative type of safety paper.

Referring to Figs. 1, 2 and 3, the safety paper comprises a subsurface layer which may be made of any suitable material, e. g., of some desired paper stock. In the embodiment shown in .Figs. 1,2 and 3,.the subsurface layer I0 is of a dark color, e. g., dark blue. Overlying the subsurface layer I0 is a surface layer H. For the purposes of affording one illustration of this invention, this surface layer may be composed of a mixture of clay and casein of the type which is commonly used in the finishing of book papers and printing papers. The surface layer includes a plurality of areas or portions l2 which, as shown in the drawing, may be in the form of suitable legends or indicia. These indicia comprise a sealing material. The sealing material may be a waterproofing material such as a clear lithe-varnish which does not substantially modify the color of the surface layer and which is insoluble in an aqueous testing liquid. For the purpose of illustration, the surface layer l I is white and the indicia l2 are likewise white and are substantially invisible when the paper is in a dry state. When it is stated that the paper is dry, it is understood that complete desiccation is not necessarily indicated but that a state of dryness which occurs after exposure or drying under normal atmospheric conditions is intended. The paper may or may not carry permanent legends l8 or decorativefigures ,20 of usual character.

The character of the paper when it is in a dry condition and. when the indicia are substantially invisible thereon is indicated in Fig. 1. Fig. 2 illustrates the appearance of the paper after a portion of the surface layer has been moistened with water, for example. The portion of the surface layer which is occupied by the indicia I2 is substantially unaffected by moistening. However, the other portion l3 of the surface layer to which the water has been applied becomes permeable to light so that the colored base layer is clearly visible therethrough. This causes the indicia l2 to stand out in relief against a background of dark color. Moreover, if the permanent legends I8 and decorative figures are of a dark color, they will become of decreasing prominence as the dark background becomes more visible and especially so if they are of substantially the same color as the color of the background (e. g., dark blue). By making these indicia I8 and 2|] of about the same color appearance as the color appearance of the portion l3 after the surface layer II has been tested by application of a liquid thereto, these indicia will become scarcely visible at all except where they overlie the indicia l2, thus affording a further safety feature.

A paper of the type illustrated in Figs. 1, 2 and 3 may be manufactured by first preparing the subsurface layer. The character of this layer and. the method of its manufacture will vary, depending on the type of safety paper that is desired. Any suitable material can be used for the subsurface layer, although fibrous materials in the form of paper are ordinarily preferable. If a relatively thin safety paper is desired, the subsurface layer is made up by any suitable paper-making operation so as to have the requisite thinness. If the safety paper is to be used in the manufacture of cartons, for example, it may be made up of relatively heavy material. The subsurface layer preferably includes a coloring matter such as a suitable dye or pigment. Such coloring matters may comprise any of the anilin dyestuffs which are well known for use in paper making and may comprise insoluble pigment coloring matters such as those used in paper making, e. g., ultramarine, carbon black, Prussian blue, burnt umber, etc. 1

After the subsurface layer has been prepared, there is applied thereto the surface layer of coating composition which comprises, for example, a clay-casein mixture such as a mixture containing four parts of clay and one part of casein. Preferably, enough of the coating composition is used so as to substantially completely obscure the subsurface layer. Moreover, excess beyond what is necessary to obtain the desired degree of invisibility of the subsurface layer is ordinarily not used so as to retain in the surface layer as much permeability to light as possible when the surface layer is treated with a testing liquid.

Mixtures of casein and clay have the property when dry of being substantially impermeable to light but of becoming highly permeable to light when moistened with water. In addition to mixtures of casein and clay, other compositions suitable for a similar purpose in the practice of this invention may be used. Thus, instead of casein, other materials may be used as albumin, glue, rosin dissolved in alkali, gum arabic and tapioca gum, as well as various other albuminous substances and gums. Instead of clay, other finelydivided mineral fillers may be used such as lithopone, barytes, calcium carbonate, silica and asbestine. When binders of the character above mentioned are employed, it is frequently desirable to employ a hardener or insolubilizer such as formaldehyde, alum, zinc sulphate, aluminum acetate, or tannic acid that is applied to the binder either before or after formation of the surface layer. When glue or albumin is used, ammonium or potassium dichromate may be employed for this purpose. These hardeners or insolubilizers? tend to render the binder part more permanent in the finished paper and make the surface layer more resistant to smudging and washing off upon the application of a testing liquid, e. g., water. Especially when rosin dissolved in alkali is used, it is desirable to employ a hardener. In addition to the materials that have been mentioned, other similar materials may be used as the coating material for the surface layer of the safety paper which are of such character as to afford a surface layer that, because of porosity, absorptiveness or the like, is penetrable by a testing liquid without being unduly softened thereby and that contains particles which, when moistened with the: testing liquid, become more transparent or translucent. Materials of the character mentioned result in a white or nearly whitesurface layer. If a color other than white is desired, a coloring matter can be incorporated such as a dye or a pigment of a color other than white, enough being used to secure a desired shade.

It is apparent that the composite paper comprising the subsurface layer and the surface layer above described can be readily manufactured in large quantities using, for example, common paper-making operations and apparatus. The completion of safety paper embodying this invention may be readily achieved by application of the waterproofing material'to the surface layer as by an ordinary printing operation. For example, a non-pigmented or clear printing ink can be used in the application of the indicia [2. For example, a clear ink may be used consisting of Parts Litho-varnish I- 87 Cobalt drier 8 Rosin oil Clear litho-varnishes of various grades which consist essentially of linseed oil that has been bodied and thickened are well known and are suitable. for the purpose. Those which are commonly sold under the designations #00 to #3 have a viscosity well suited for the practice of this invention. In addition, oils may be added such as linseed oil, China-wood oil, rapeseed-oil, etc., either plain or modified by blowing or modified by the inclusion or incorporation of gums such as kauri gum or rosin or by the inclusion of any of the common oil-soluble waxes. The varnishes of the China-wood oil type or linseed oil type may be used and in such varnishes synthetic resins such as resins of the phenol-formaldehyde type may be used. Lacquers having as a base a soluble derivative of cellulose such as cellulose esters or ethers can be used. Likewise waxes may be used as the waterproofing material such as paraflin, beeswax, carnauba wax, Japan wax, etc., when dissolved in a volatile solvent such as naphtha, ethylene dichloride, benzine and the like. It is preferable, of course, that the. material used and its consistency be such that it is adapted for the type of printing equipment that is used in the application of the indicia to the safety paper.

It is usually preferable. to employ a sealing material which dries "fiat, i. e., without a shiny surface when the rest of the surface layer of the safety paper is not shiny so as to minimize the visibility of the sealing material in the dry surface layer. There are certain clear printing inks, varnishes and lacquers which dry to a fiat finish. When a pigment is included in the sealing material, preferably one which matches the color of the surface sheet, the pigment aids in preventing any darkening of the portion of the surface layer to which the sealing material is applied. In applying the sealing material, it should preferably be applied to the surface of the surface layer or should penetrate the surface layer somewhat less than its full thickness, as some sealing materials, if permitted to penetrate through the surface layer, cause it to become somewhat more transparent, rendering the subsurface layer permanently visible therethrough.

An alternative embodiment of this invention 1s shown in Fig. 4. In this modification of the invention, the subsurface layer l0 may be of the same character as that above described in connection with Figs. 1, 2 and 3. In the modification shown in Fig. 4, however, the surface layer l4, instead of being in the form of an applied coating composition, is in the form of a thin paper. Preferably the paper in surface layer 14 is white in color and overlies a subsurface layer which is of a relatively deep shade. In the modification herein illustrated, the surface layer l4 includes areas or portions l2 as indicated in Figs. 1 and 2, which do not have their permeability to light affected by the application of liquid, e. g., water, thereto, to as great an extent as the other portions of the surface layer. The paper of the surface layer I4 is preferably made of a lightly beaten paper stock and a substantial amount (e. g., 20 to 40%) of filler such as the fillers above mentioned and is quite thin so that, upon applying a liquid thereto, it becomes of ample, the substratum ll] of desired deep shade of color can be prepared in any suitable manner as herein above described. The layer M can be deposited on the subsurface layer Ill so as to overlie this layer. Thereafter the safety paper may be printed with a sealing material in the manner hereinabove described. Paper-making operations are well known wherein different strata of paper are successively made up and made integral with each other as by the employment of the well-known cylinder machine. Thus one or more strata of colored stock may constitute the subsurface layer I0 and one or more additional strata of paper stock which is of different color and which is preferably absorbent and heavily loaded with filler may be superimposed upon the surface layer It) in a paper-making operation. Thereafter printing with sealing material may be applied to the surface layer. Alternatively, the subsurface layer Il] may be made in one paper-making operation and the surface layer l4 made in an entirely separate paper-making operation, the two layers being subsequently united in any suitable way as by being pressed together in the wet state or being united by some suitable adhesive. When an adhesive is used, it should preferably not penetrate through the surface layer. In such case, it is possible to apply printing'with waterproofing material to the paper constituting the surface layer before it is united with the subsurface layer. It is preferable, however, to unite the surface and subsurface layers together and subsequently apply the sealing material as by printing to the composite safety paper.

A; further modification of this invention is shown in Fig. 5. In this modification, the surface layer I4 may be of the character of the layer l4 described above in connection withFig. 4. The surface layer 14 contains fibrous material or other bonding material which imparts sufficient structural strength to this layer so that the safety paper is suitable for use as a label, for example. The'subsurface layer [9 in this modification comprisesa colored coating having the color contrast with the surface layer of the character herein described. The surface layer l4 carries the indicia [2 which are applied thereto by depositing -a sealing material of the character above mentioned at or adjacent the outer surface of the surface layer.- The layer 19 may be in the form of some suitable, paint, lacquer, ink, or dye. For example, the layer IS could be a colored oil ink or a coating comprising a pigment ofdesired color carried in casein as a binder. When it is desired that the safety paper be in the form of a label, for example, carrying an adhesive on the back thereof, the layer I9 may include an adhesive colored with a pigment. For example, the layer l9 may comprise a dextrine adhesive which is highly colored by a pigment or dye to afford a background having a marked color contrast in comparison with the color of the surface layer M.

In the manufacture of the embodiment shown in Fig. 5, a paper adapted to haveits permeability to light increased upon application of a liquid thereto is prepared and is printed upon with a sealing material such as a litho-varnish which does not result in substantial change of color where it is applied to the surface layer. The back of the paper thus prepared may then have a coating of colored material applied thereto. When this coating is in the form of a colored adhesive, conventional gumming machinery may be used for this purpose. Of course, the coating may be applied to the back of the paperprior to applying the sealing material thereto in the form of indicia.

In Fig. 6, a further modification is shown in which the subsurface layer [5 has a backing member [6 integral therewith. The surface layer I! may be of the character of the layer II in Fig. 3 (or the layer I4 in Fig. 4), for example. When the subsurface layer has a backing layer integral therewith, the subsurface layer can be made without regard to its structural strength. For example, the subsurface layer may be in the form of a very thin web of paper or other sheetlike material. Alternatively, the layer l5 may be in the form of a coating such as the coating l9 described above in connection with Fig. 5 which is initially applied to the back of the surface layer. The layer l5 likewise may be in the form of a coating such as paint, lacquer, ink or dye which is applied to the surface of backing Hi.

In the foregoing drawing, no attempt has been made to indicate material which may, if desired, be applied to the back of the safety paper. If desired, an adhesive material, for example, such as gum, glue, dextrine or the like, may be applied to the back of layer I0 in Figs. 3 and 4 and to the back of layer 16 in Fig. 6. In the manufacture of labels, for example, it is frequently desirable that the labels be preformed with an adhesive on the back, so that the safety paper can be readily affixed to the surface of a body. Moreover, if the layer I9, in Fig. 5, does not comprise an adhesive, an additional coating of adhesive may be applied to the back of layer I9. Alternatively, the paper may be made with a layer such as the layers H and [4, not only on one side, but on both sides thereof, where it is desired to have paper which can be tested on both sides for its authenticity. For example, the paper shown in Figs. 3 and 4 may have the layers II and M on both sides of the layer l0, instead of on one side only thereof.

As aforesaid, it is usually desirable that the surface layer be white in color and that the subsurface layer be of a relatively deep shade of color. However, it is apparent that certain features of this invention may be availed of when the subsurface layer and the surface layer are of contrasting colors and both are of colors other than white. By contrasting colors, it is to be understood that the colors of the different layers may be different, e. g., the subsurface layer may be blue and the surface layer may be red; or that the subsurface layer and surface layer may be different shades of the same color, e. g., the subsurface layer may be a dark blue while the surface layer is of a lighter shade of blue. It is preferable, as aforesaid, that the subsurface layer be of a darker shade than the surface layer. By this, it is meant that the surface layer is either white or more nearly white than the subsurface layer.

A safety paper having a preferred illustrative color combination according to this invention may comprise a subsurface layer which is dark blue with a white surface layer. Alternatively, the subsurface layer may be black and the surface layer a light shade of buff. As a further illustration, the subsurface layer may be red and the surface layer a light shade of red, e. g., pink. In the illustrations just given, the subsurface layer and surface layer are to be regarded as being of contrasting color, the deeper shade of color being in the subsurface layer.

It is normally preferable that the surface layer be of a character which is adapted to have its permeability to light increased when moistened with water. However, other liquids than water may be used by which to test the paper. Thus saliva is to be regarded as the equivalent of water. Likewise various dilute aqueous solutions of acids or salts may be applied as the testing liquid. By way of further illustration, where the surface layer is made of a mixture of binder and filler, e. g., casein and clay, or is made of a thin sheet of absorbent, opaque paper, of the character aforesaid, other liquids than water may be used to increase the permeability of the portions of the surface layer which have not been treated with a sealing material. Thus various liquids such as ethyl, methyl and butyl alcohols, ethyl acetate, carbon tetrachloride, benzol, turpentine. and the like, may be used with which to test the paper. may be used, such a liquid has the disadvantage that it is non-volatile and leaves a permanent mark on the paper. Preferably, a volatile liquid such as water, alcohol, carbon tetrachloride or the like, is used which quickly evaporates after While anoil such as a light mineral oil the paper has been tested by application, of such liquid thereto. It is also preferable that the index of refraction of the particles of filler material and of the testing liquid be as nearly as possible the same, as the transparency of the surface layer can be increased to a greater extent when a testing liquid of such character is selected. However, even when there is quite a wide difference between the index of refraction of the filler particles and the index of refraction of the testing liquid, very pronounced increase in transparency of the surface layer can be obtained.

It is preferable that the sealing material deposited on or in portions of the surface layer to render such portions less affected as to light permeability when treated with a testing liquid, be substantially insoluble in the testing liquid that is to be used. For example, when water is the testing liquid, some sealing material which is insoluble in water, is preferably used. This is not essential, however, as the testing liquid is normally applied only for a few moments and a test ordinarily takes insufiicient time to permit extensive solution of such-materials as are incorporated in varnishes and the like even though the testing liquid might in time dissolve such materials. As a matter of fact, varnishes, lacquers, drying oils and the like are waterinsoluble. .While such substances may be slowly soluble in certain solvents therefor, the testing of the paper does not require sufficient time to result in substantial dissolving out of such sealing materials. It is likewise preferable that the testing liquid be of such character as not to dissolve the binder for the surface layer excessively rapidly so as to cause the surface layer to smudge to an undesirable extent.

While this invention has been described in connection with certain illustrative embodiments thereof, it is to be understood that this has been merely for the purpose of affording illustrations of this invention, and that the scope of this invention is to be limited only by the language of the following claims.

We claim:

1. A safety paper which comprises a surface layer and a sub-surface layer of a color which contrasts with the color of said surface layer, a first portion of said surface layer being adapted to become substantially more permeable to light when said portion in a dry state has a liquid applied thereto so that the color of said subsurface layer is visible therethrough, and a second portion of said surface layer which is contiguous with said first portion and is of substantially the same color as said first portion being adapted when said second portion in a dry state has said liquid applied thereto to have its permeability to light substantially less affected than said first portion.

2. A safety paper which comprises a surface layer and a sub-surface layer of a color which contrasts with the color of said surface layer and is other than white, a first portion of said surface layer being adapted to become substantially more permeable to light when said portion is moistened with water so that the color of said sub-surface layer is visible therethrough and a second portion of said surface layer which is contiguous with said first portion and which is of substantially the same color as said first portion being adapted when moistened with water to have its permeability to light substantially less affected than said first portion.

3. A safety paper which comprises a surface layer and a sub-surface layer of a color which contrasts with the color of said surface layer and is other than white, a first portion of said surface layer being adapted to become substantially more permeable to light when said first portion in a dry state has a liquid applied thereto so that the color of said sub-surface layer is visible therethrough and a second portion of said surface layer which is contiguous with said first portion and which is of substantially the same color as said firstportion when said surface layer is in a dry state including a sealing material which prevents said second portion of said surface layer from becoming as permeable to light as said first portion when said liquid is applied to said surfacelayer.

4. A safety paper which comprises a surface layer and a sub-surface layer of a color which contrasts with the color of said surface layer and is other than white, a first portion of said surface layer being adapted to become substantially more permeable to light when said portion in a dry state is moistened with water so that the color of said sub-surface layer is visible therethrough, and a second portion of said surface layer which is contiguous with said first portion and which is of substantially the same color as said first portion when said surface layer isin a dry state containing a waterproofing material including a pigment which prevents said second portion of said surface layer from becoming as permeable to light as said first portion of said surface layer upon being moistened with water.

5. A safety paper which comprises a surface layer and a sub-surface layer of a color other than white which contrasts with the color of said surface layer and is substantially deeper in shade, a first portion of said surface layer being sufficiently impermeable to light so that the color of said sub-surface layer is substantially nondiscernible when saidsurface layer is dry and being adapted upon application of a liquid thereto to become permeable tolight so that the color of said sub-surface layer is discernible therethrough and a second portion of said surface layer which is of substantially the same color as said first portion when said surface layer is dry and which is substantially impermeable to light so that the color of said sub-surface layer is substantially non-discernible therethrough when said surface layer is dry containing a sealing material which is adapted to prevent said second portion from having its. permeability to light increased upon application of said liquid thereto to as great an extent as said first portion.

6. A safety paper which comprises a surface.

layer and a sub-surface layer of a color other than white which contrasts with the color of said surface layer and is substantially deeper in shade, a first portion of said surface layer being sufficiently impermeable to light so that the color of said sub-surface layer is substantially non-discernible when said surface layer is dry and being adapted upon moistening with water to become permeable to light so that the color of said sub-surface layer is discernible therethrough, a second portion of said surface layer which is contiguous with said first portion and which is of substantially the same color and opacity as said first portion when said surface layer is dry containing a Waterproofing material that is adapted to prevent said second portion from becoming substantially more permeable to light when moistened with Water.

'7. A safety paper which comprises a surface layer of substantially white material and a subsurface layer of material of a color other than white, said surface layer when dry being sufficiently opaque to substantially conceal the color of said subsurface layer, the material of said surface layer being adapted to have increased permeability to light when moistened with water so that the color of said subsurface layer is visible therethrough except at a plurality of areas in the form of indicia which are of material that is substantially less affected in its permeability to light upon being moistened with water.

8'. A safety paper which comprises a fibrous subsurface layer of a colorother than white and a surface'layer of a coatingcomposition which comprises a finely-divided mineral material and a binder integral with said subsurface layer which is of a color that contrasts with the color of said subsurface layer and is of a lighter shade than that of said subsurface layer, said surface layer comprising a first portion that is adapted to have its permeability to light substantially increased upon application of aliquid thereto so that the color "of said subsurface layer is visible there- 1 through and a second portion in the form of a plurality of indicia that is adapted to have its permeability to light affected to a substantially lesser degree than said first portion upon application of said liquid thereto by virtue of the inclusion of a sealing materialatherein.

91 A safety paper'whichi comprises a subsurface layer and: a surface layer of fiber-containing material integral with saidsubsurface layer, said subsurface layer comprising an. adhesive which is 1 colored other than white and which isadapted to bond the safety paper to; the surface of a body, said surface layerbeing of a color which contrasts with the color of said subsurfacelayer and is of a lighter shade than said subsurface layer and said surface layer comprising a first portion that is adapted to have its permeability to light substantially increased upon application of a liquid thereto sothat said subsurface layer is visible therethrough and a second portion that is adapted tohave its permeability to light affected to a substantially lesser degree than said first portion upon application of said liquid thereto.

10. A safety paper which comprises a subsurface layer of a color other than white and a sur- :face layer of fiber-containing material which is in the form of a colored coating underlying said surface layer, and said surface layer comprising a first portion that is adapted to. have its permeability to light substantially increased upon application of a liquid thereto so that said subsurface layer is visible therethrough and a second portion that is adapted to have its permeability to light affected to a substantially lesser degree than said first portion upon application of said liquid thereto by virtue of the inclusion of a sealing material therein.

11. A safety paper which comprises a surface layer, a subsurface layer of a color other than white which contrasts with the color of said surface layer and is of substantially deeper shade, and material overlying a portion. of saidv surface layer, said surface layer including a portion contiguous with said material which isadapted upon application of a liquid thereto to become substantially more permeable to light so that the. color of said, subsurface. layer is visible theresurface layer visible therethrough, so that the color of said material contrasts with the color appearance of said surface layer when said surface layer is dry and is substantially non-dis-' cernible when said surface layer has a liquid applied thereto.

12. A safety paper which comprises a surface layer that is substantially white appearing when dry, a subsurface layer of a color other than white which contrasts with the color of said surface layer, and material which overlies a portion of saidsurface layer and which is of a color corresponding substantially to the color of said subsurface layer, said surface layer including at least, a portion thereof which is contiguous with said material and which is adapted upon application of a liquid thereto to become substantially more permeable to light so that the color of said subsurface layer is visible therethrough. 7

13. In a method of making safety paper, the step of making a composite sheet comprising a subsurface layer and a surface layer of material which is of a color contrasting to the color of said subsurface layer and which has substantially less permeability to light when dry than after a liquid has been applied thereto and the step of applying to material in a portion of said surface layer a sealing material which does not substantially alter the color of said material of said surface layer when in a dry state and which substantially decreases the extent to which the permeability to light of said material of said surface layer is increased by treatment with said liquid, said sealing material not being applied to another portion of said surface layer.

- 14. A method of making safety paper which comprises making a composite sheet comprising a subsurface layer of a color other than white and a surface layer of material which is of contrasting color and of lighter shade in comparison with the material of said subsurface layer and which is adapted to have the permeability thereof to light substantially increased by application of a liquid thereto so that the color of said subsurface layer is visible through said surface layer, and then printing a. plurality of indicia upon said surface layer with a sealing material which substantially decreases the extent to which the permeability to light of said material of said surface layer is increased by application of said liquid thereto and which does not substantially alter the color of said surface layer when in a dry state.

15. A method of making safety paper which comprises making a sheet of material at least the surface of which is colored a color other than white to constitute a colored subsurface layer of said paper, disposing over said subsurface layer in integral relation thereto a surface layer of material which is of contrasting color and of lighter shade in comparison with the color of said subsurface layer and which is adapted to have the permeability thereof to light increased by application ofaliquidthereto so that the color of said subsurface layer is visible through said surface layer, and applying to a portion of said surface layer a sealing material which does not substantially alter the color of said material of said surface layer when in a dry state and which substantially decreases the extent to which the permeability tolightof said materialof said first layer is increased by application of said liquid thereto, said sealing material not being applied to another portion of said surface layer.

16. A method of making safety paper which comprises making a first fibrous sheet of material at least the surface of which is colored a color other than white as a colored subsurface layer of said paper, making a second sheet of material containing fiber and mineral filler which is of a contrasting color and of lighter shade in comparison with the color of said first sheet and which has substantially less permeability to light when dry than after a liquid has been applied thereto, uniting said first and second sheets with said second sheet as a surface layer and then printing upon said surface layer a plurality of indicia with a sealing material which does not substantially alter the color of said surface layer when in a dry state and which substantially decreases the extent to which the permeability of said surface layer to light is increased by application of said liquid thereto.

17. A method of making safety paper which comprises making a fibrous sheet of material at least the surface of which is colored a color other than white to constitute a colored subsurface layer of said paper, applying a coating composition to said subsurface layer, which coating composition is of material that is of a contrasting color and of a lighter shade in comparison with the color of said subsurface layer and which has substantially less permeability to light when dry than after a liquid has been applied thereto and then printing upon said surface layer a plurality of indicia with a sealing material which does not substantially alter the color of said surface layer when in a dry state and which substantially decreases the extent to which the permeability of said first layer to light is increased by application of said liquid thereto.

18. A method of making safety paper which comprises making a sheet of fiber-containing material which is adapted to have the permeability thereof to light substantially increased upon the application of a liquid thereto, applying sealing material to a portion of said sheet, which sealing material does not substantially alter the color of said sheet and which substantially decreases the extent to which the permeability to light of said sheet is increased by application of said liquid to another portion of said sheet, and then depositing a layer of colored material in integral relation with one face of said sheet, the color of said colored material being of contrasting color and of darker shade in comparison with the color of said sheet.

19. A method of making safety paper which comprises making a first sheet of material at least the surface of which is colored a color other than white to constitute a colored subsurface layer of said paper, making a second sheet of material which is of contrasting color and of lighter shade in comparison with the color of said subsurface layer to constitute a surface layer of said paper, applying to said second sheet in the form of a plurality of indicia a sealing material which does not substantially alter the color of said material of said second sheet when in a dry state and which substantially decreases the extent to which the permeability to light of said material of said second sheet is increased by application of said liquid thereto, and then uniting said second sheet with said first sheet as a surface layer overlying said surface of said first sheet.

20. In a method of making safety paper, the

step of making a composite sheet comprising a surface layer which contains fiber and mineral filler and which has substantially less permeability to light when dry than after a liquid has been applied thereto and as a subsurface layer a colored coating integral with the back of said surface layer, the color of said coating being other than white and being of a color which contrasts with and is of darker shade in comparison with the color of said surface layer, and the step of applying in the form of indicia a sealing material to a portion of said surface layer which does not substantially alter the color of said material of said surface layer when in a dry state and which substantially decreases the extent to which the permeability to light of said material of said surface layer is increased by treatment with said liquid, said sealing material not being applied to another portion of said surface layer.

FRANCIS L. SIMONS. MARK W. WEISS.

CERTIFICATE OF-CORRECTION. Patent No. 2,129,562. September 6, 19

FRANCIS L. SIMONS, ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows; Page 1, first column, line 35, for "is" read it; page 5, first column, line 5h, for the word g"add'ed" read nsed; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office. Y

Signed and sealed this 22nd day of November, Ac D. 1958 [Herw Yen Marie (Seal) Acting Commissioner of Patents. 

